Pilot Aided Data Transmission and Reception with Interference Mitigation in Wireless Systems

ABSTRACT

Embodiments disclosed herein reduce interference at pilot symbols and also enable good interference measurements by using a combination pilot tones and null tones along with null tones. In this type of system, the receivers can estimate tile channel state information without any interference from the remaining transmitters and at the same time the receiver can measure either the individual interference channel states or the interference covariances from the silent periods. The groups of transmitters are reused in geographically separated region using a frequency reuse structure. In a preferred implementation, pilot signal is precoded using a multi-antenna precoder. The precoder may be same for pilot and data.

This application claims priority from Indian provisional applications:427/CHE/2009 titled “Data Collision Avoided Interlaced Pilots”,1930/CHE/2009 titled “Collision free interlaced pilot patterns and pilotsequences”, 2093/CHE/2009 titled “Downlink Pilots and Data Transmissionin OL MIMO Region”, 2095/CHE/2009 titled “Rank one Region in WirelessSystems for Interference Mitigation, and 2815/CHE/2009 titled “CDR andPilot Specification in OL Region”.

TECHNICAL FIELD

This invention relates to wireless communications and more particularlyto pilot design with interference mitigation in wireless systems.

BACKGROUND

A wireless network generally comprises of many smaller cells to coverthe whole service area. Each cell is further divided into multiplesectors. Each cell/sector may have a base station (BS) and multiplemobile stations (MSs). Cellular system with 3-sectors per cell isdepicted in FIG. 1. The MSs in a sector may be fixed, nomadic or mobile.Communication from a BS to an MS is called as downlink or forward link.Similarly, communication from an MS to a BS is called as uplink orreverse link. In IEEE 802.16m system a BS is denoted as advanced BS(ABS) and an MS is denoted as advanced MS (AMS). Similarly inLTE/LTE-Advanced a BS is denoted as e-NodeB and a MS is denoted as UE.

The IEEE 802.16m, LTE and LTE-Advanced are broadband wireless standardsthat use Orthogonal Frequency Division Multiplexing Access (OFDMA)technology in the downlink. The block diagram of an OFDMA based systemis shown in FIG. 2. The IEEE 802.16m uses OFDMA, and theLTE/LTE-Advanced use DFT spread OFDMA (a.k.a. SCFDMA) technology in theuplink.

In the IEEE 802.16m, LTE and LTE-Advanced standards, resources areallocated in a time-frequency grid called a resource block (RB) orphysical resource unit (PRU) that consists of P subcarriers and Q OFDMsymbols or multiples of P subcarriers and Q OFDM symbols. The value of Pand Q can be any integer, and the value of P and Q are dependent on theindividual standards. The P subcarriers can be physically contiguous ordistributed, and in case of distributed, permutation can be subcarrierwise or groups of subcarrier wise.

In the downlink, one or more RBs may be intended for single or group ofusers; in the uplink, a transmitter may be assigned one or more RBs andseveral transmitters may transmit simultaneously. The PSK/QAM input dataare mapped to distinct subcarriers, and filled with zeros in the unusedsubcarriers before taking an N-point IDFT.

When the P subcarriers are adjacent, it is possible to do ChannelDependent multi-user Scheduling (CDS) and improve the throughput of thesystem. In CDS, users requesting resources with good channel quality aregiven preference in scheduling. In distributed modes, the P subcarriersare distributed over the entire available bandwidth (for instance, in apseudo-random fashion that can include fast hopping across the tones)and interference from adjacent tones is averaged and frequency diversityis exploited inherently.

The localized resource unit, also known as Contiguous Resource Unit(CRU) contains a group of subcarriers which are contiguous across thelocalized resource allocations. The minimum size of the CRU equals thesize of the PRU, i.e., P subcarriers by Q OFDMA symbols. The resourceallocated to a user or a group of users will be in multiples of thebasic resource units, and it can be either contiguous or distributed. N1contiguous basic resource units are called as sub-band, and N2contiguous resource units are called as mini-band in IEEE 802.16mstandards. N1 and N2 are positive integers. Typical number for N1 is 3,4 or 5 and N2 is 1 or 2. The miniband CRUs available in a frequencypartition can be divided into two groups. The first group can be used asminiband CRU itself, and the second group will be used to createsubcarrier, or pairs of subcarrier, groups of subcarrier (tile) permuteddistributed resource unit (DRU).

In the IEEE 802.16m systems, the total available physical resource isdivided into logical resources to support scalability, multipleaccesses. The logical resources are called as Logical Resource Units(LRU), and each LRU is composed of 18 contiguous CRU or pair-wisesubcarrier permutation over the entire available bandwidth (DRU) and Qcontiguous OFDM symbols. When LRU is composed of CRU, each LRU isfurther divided into miniband CRU (NLRU) with N2=1 and consisting of 18contiguous subcarriers and subband CRU (SLRU) with N1=4 and consistingof 72 contiguous subcarriers. When the DRU is derived from NLRU, the LRUis called as Distributed Logical Resource Unit (DLRU), and the LRUconsists of 18 subcarriers. In IEEE 80216m systems, the DLRU contains agroup of paired subcarriers spread across the distributed resourceswithin a frequency partition. The minimum unit for forming the DLRU isequal to a pair of subcarriers, called tone-pair.

FIGS. 4 and 5 illustrate examples of RB or PRU structure used indownlink of the IEEE 802.16m standards. In every PRU, certainsubcarriers are reserved for pilot tones and the pilot tones used forestimating the channel between the transmitter and receiver. In OFDMAsystems, the localized and distributed sub-channelization methodsprovide a great flexibility in reaping the benefits of both single userand multi-user diversity.

The advanced air interface basic frame structure is illustrated in FIG.3. Each 20 ms superframe is divided into four equally-sized 5 ms radioframes. When using the channel bandwidth of 5 MHz, 10 MHz, or 20 MHz,each 5 ms radio frame further consists of eight Advanced Air Interface(AAI) subframes for G=1/8 and 1/16. For G=1/4, the 5 ins radio frameconsists of seven AAI subframes. With the channel bandwidth of 8.75 MHz,the 5 ms radio frame consists of seven AAI subframes for G=1/8 and 1/16,and six AAI subframes for G=1/4. With the channel bandwidth of 7 MHz,the 5 ms radio frame consists of six AAI subframes for G=1/16, and fiveAAI subframes for G=1/8 and G=1/4. An AAI subframe shall be assigned foreither DL or UL transmission. There are four types of AAI subframes:

1) type-1 AAI subframe which consists of six OFDMA symbols,

2) type-2 AAI subframe which consists of seven OFDMA symbols,

3) type-3 AAI subframe which consists of five OFDMA symbols, and

4) type-4 AAI subframe which consists of nine OFDMA symbols. This typeshall be applied only to an UL AAI subframe for the 8.75 MHz channelbandwidth when supporting the Wireless MAN-OFDMA frames. The size of Qdepends on the AAI subframe types as mentioned above.

The basic frame structure is applied to FDD and TDD duplexing schemes,including H-FDD AMS operation. The number of switching points in eachradio frame in TDD systems shall be two, where a switching point isdefined as a change of directionality, i.e., from DL to UL or from UL toDL. When H-FDD AMSs are included in an FDD system, the frame structurefrom the point of view of the H-FDD AMS is similar to the TDD framestructure. However, the DL and UL transmissions occur in two separatefrequency bands. The transmission gaps between DL and UL and between ULand DL are required to allow switching the TX and RX circuitry.

A data burst shall occupy either one AAI subframe (i.e. the default TTItransmission) or contiguous multiple AAI subframes (i.e. the long TTItransmission). Any 2 long TTI bursts allocated to an AMS shall not bepartially overlapped, i.e. any 2 long TTI bursts in FDD shall either beover the same 4 subframes or without any overlap. The long TTI in FDDshall be 4 AAI subframes for both DL and UL. For DL (UL), the long TTIin TDD shall be all DL (UL) AAI subframes in a frame.

The transmission, of predefined (known) sequences on the pilotsubcarriers in the downlink is necessary for enabling channelestimation, measurements of channel quality indicators (CQI) such as theSINR, frequency offset estimation, etc. To optimize the systemperformance in different propagation environments and applications, AAIof IEEE 802.16m supports both common and dedicated pilot structures. Thecategorization in common and dedicated pilots is done with respect tothe usage of common and dedicated pilots. The common pilots can be usedby all MSs and the pilots are precoded in the same way as the datasubcarriers within the same PRU. Dedicated pilots can be used with bothlocalized and distributed allocations. The dedicated'pilots areassociated with a specific resource allocation and are intended to beused by the MSs allocated to said specific resource allocation.Therefore dedicated pilots “shall be precoded or beamformed in the sameway as the data subcarriers of the resource allocation. The pilotstructure is defined for up to eight transmission (Tx) streams and thereis a unified pilot pattern design for common and dedicated pilots. Thereis equal pilot density per Tx stream, while there is not necessarilyequal pilot density per OFDMA symbol of the downlink AAI subframe.Further, within the same AAI subframe there is equal number of pilotsfor each PRU of a data burst assigned to one MS. Pilot patterns arespecified within a PRU. The base pilot patterns used for two DL datastreams in dedicated and common pilot scenarios are shown in FIG. 4,with the subcarrier index increasing from top to bottom and the OFDMsymbol index increasing from left to right. Subfigure (a) and Subfigure(b) in FIG. 4 shows the pilot location for pilot stream 1 and pilotstream 2 in a PRU, respectively. The number on a pilot subcarrierindicates the pilot stream the pilot subcarrier corresponds to. Thesubcarriers marked as ‘X’ are null sub-carriers, on which no pilot ordata is transmitted. The interlaced pilot patterns are generated bycyclic shifting of the base pilot patterns. The interlaced pilotpatterns are used by different BSs for one and two streams. Interlacedpilot patterns for one stream is shown in FIG. 5 and interlaced pilotpatterns on stream 1 and stream 2 for two streams are shown in FIG. 6and FIG. 7, respectively. Each BS chooses one of the three pilot patternsets (pilot pattern set 0, 1, and 2) as shown in FIG. 5, FIG. 6 and FIG.7. The index of the pilot pattern set used by a particular BS with CellID=k is denoted by p_(k). The index of the pilot pattern set isdetermined by the Cell ID according to the following equation:p_(k)=floor (k/256).

For one stream, each ABS additionally chooses one of the two stream sets(stream set 0 and 1) within each pilot pattern set. The index of thestream, denoted by s_(k), shall be determined according to the followingequation: s_(k)=mod (k, 2). For the AAI subframe consisting of 5symbols, the last OFDM symbol in each pilot pattern set shown in FIG. 4is deleted. For the AAI subframe consisting of 7 symbols; the first OFDMsymbol in each pilot pattern set shown in FIG. 4 is added as 7th symbol.

Communication between the BS and the MS and vice-versa requiresspectrum. Spectrum is a very scarce resource, and the spectrum furtherlimited due to pre-occupation of some portion of the bands for otherapplications such as defense and space in some countries. The availablespectrum will be reused in every cells/sectors. Since same frequencyband (bandwidth) is reused in different cells/sectors depending on thereuse factor, the subscriber at the boundary between regions will beseverely affected by interference. This phenomenon is called asco-channel interference (CCI), and the performance for the subscriber inthese cell edge regions is severely affected by the CCI. Thispredominantly limits the cell edge throughput, and hence brings down theoverall system throughput. The problem is even worse in the case of theemerging broadband wireless technologies such as IEEE 802.16m, LTE andLTE-Advanced, where the available frequency resource is expected to beused in a frequency reuse 1 fashion in every sector in order to meet thehigh data rate requirements of the subscribers. Therefore, the majorchallenge in developing the above mentioned emerging broadband wirelesstechnologies is to mitigate interference.

Interference can be mitigated using simple receiver processingtechniques like interference suppression minimum mean square error(MMSE) receivers. There is another interference mitigation techniquecalled conjugate data repetition (CDR), where a transmission schemerepeats data in a predefined fashion across cells/sectors relying onmultiple copies of the transmitted signal, multiple receive antennas,and MMSE receivers. The techniques can be employed to suppressinterference, and thereby improve the reliability as well as throughputfor cell edge users.

One of the major challenges in the design of interference suppressionMMSE receiver is to obtain a good quality estimation of the desiredfading channel and the ‘interference plus noise’ covariance matrix. Thereference signals or pilots are transmitted by the base station (BS) orby the MS for the purpose of channel estimation, and also for theinterference plus noise covariance estimation. In the interferencelimited scenario, because of the frequency reuse, these reference signalor pilots will also be affected by severe CCL This in turn affects thequality of channel estimates and interference covariance estimates,which in turn affect the throughput of the cell edge users.

Consider a cellular layout with 3 sectors cells as shown in FIG. 1. Ingeneral, the strongest interference for a cell edge user comes fromthose sectors with sector numbers different from its desired one. Forexample in FIG. 1, the user with sector number 0 receives the strongestinterference from those surrounding sectors with sector numbers 1 and 2.

The SINR seen by the pilot symbols can be improved by avoiding pilot topilot collisions between sectors with different sector numbers usinginterlaced pilots. Each sector number is assigned a pilot pattern, in aset of locations in the 2-dimensional frequency-time grid within a PRU,which does not collide with those used by other sectors with differentsector number. For example in IEEE802.16m, pilot pattern used by sector0 is shown in FIG. 4. The Sector 1 and Sector 2 use cyclically shiftedversion of the pilot pattern used by sector 0 as shown in FIGS. 5, 6 and7. The SINR seen by the pilot symbols can also be improved by boostingthe power of pilot tones with respect to data tones. The pilot tonesreceive interference from the data tones of the neighboring sectors. Thepilot boosting helps to improve the receivedsignal-to-interference-plus-noise-ratio (SINR) of the pilot tones.

The pilot tones are boosted at the expense of data tone's power. Thepower on data tones has to be reduced to keep the total transmittedpower the same. This reduces data SINR and results in higher error rate.The data tones transmitted at the locations corresponding to the pilotpositions of the neighboring sectors see heavy interference resulting indata erasures. The interference covariance estimates measured from pilottones are not accurate since the number of pilots within a PRU is smallto get enough averaging. Moreover, the interference covariance of thosedata tones interfered by pilot tones are different from those interferedby data tones. The interference suppression receivers may not workefficiently with the conventional techniques.

Another aspect affecting the reliability of CQI (for example thepost-processing MMSE SINR estimates) measurement is the multi-antennaprecoder used at the transmitter. When the desired signal as well asinterfering signals employ multiple antennas for transmission, thesignal as well as interference measured at the receiver become afunction of the multi-antenna precoder employed at the respectivetransmitters which vary in frequency and time continuously based on thefeedback from the respective receivers. In systems employing closed-loopprecoded transmission, the CQI changes from time to time. This change inCQI causes the multi-user scheduler to allocate incorrect modulation andcoding rate (MCS) and therefore causes degradation in system capacity.

The IEEE 802.16m standard uses open-loop (OL) region in the downlink.The OL region is defined as a time-frequency resource using a givenpilot pattern and a given open-loop MIMO mode without closed loop rankadaptation. The open-loop region allows base stations across differentcells/sectors to coordinate their open-loop MIMO transmissions, in orderto offer a stable interference environment where the precoders andnumbers of streams are not time-varying. The resource units used for theopen-loop region are indicated in a downlink broadcast message and theresource units shall be aligned across cells.

The DL OL region consists of a rank-1 OL MIMO region where only a singledata stream is transmitted across multiple antennas and uses singlestream rank-1 OL precoding. The precoder is kept constant for theduration of the resource block (RB) or groups of RBs and the precodermay change from one (or group of) resource block to another. In OLregion, the precoder that is used in each RB is pre-defined. Data andpilots in each RB are precoded using the same precoder.

SUMMARY

An object of this invention is to propose a simple way of reducinginterference at pilot symbols, enable good interference measurements,enable efficient interference suppression receivers, accurate channelquality information (CQI) estimation based on post-processed SINR andenable accurate and efficient multi-user scheduling for CDR and non-CDRmodes operating in rank-1 OL region. However, this invention is notlimited to the rank-1 OL region.

These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments and numerous specific details thereof, are givenby way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments hereinwithout departing from the spirit thereof, and the embodiments hereininclude all such modifications.

BRIEF DESCRIPTION OF DRAWINGS

This invention is illustrated in the accompanying drawings, throughoutwhich like reference letters indicate corresponding parts in the variousfigures. The embodiments herein will be better understood from thefollowing description with reference to the drawings, in which:

FIG. 1 illustrates a cellular layout with 3 sector cells, according toan embodiment herein;

FIG. 2 illustrates a block diagram of an OFDMA based system, accordingto an embodiment herein;

FIG. 3 illustrates the basic frame structure for 5, 10 and 20 MHzchannel bandwidths, according to an embodiment herein;

FIG. 4 illustrates pilot patterns used for 2 DL data streams, accordingto an embodiment herein;

FIG. 5 illustrates interlaced pilot patterns for 1 data stream outsidethe open-loop region, according to an embodiment herein;

FIG. 6 illustrates interlaced pilot patterns on stream 0 for 2 datastreams, according to an embodiment herein;

FIG. 7 illustrates interlaced pilot patterns on stream 1 for 2 datastreams, according to an embodiment herein;

FIG. 8 illustrates COFIP pilot structure for pilot pattern set 0 for AASsubframe with 6 OFDM symbols, according to an embodiment herein;

FIG. 9 illustrates COFIP pilot structure for pilot pattern set 1 for AASsubframe with 6 OFDM symbols, according to an embodiment herein;

FIG. 10 illustrates COFIP pilot structure for pilot pattern set 2 forAAS subframe with 6 OFDM symbols, according to an embodiment herein;

FIG. 11 illustrates COFIP pilot structure for pilot pattern set 0 forAAS subframe with 5 OFDM symbols, according to an embodiment herein

FIG. 12 COFIP illustrates pilot structure for pilot pattern set 1 forAAS subframe with 5 OFDM symbols, according to an embodiment herein

FIG. 13 illustrates COFIP pilot structure for pilot pattern set 2 forAAS subframe with 5 OFDM symbols, according to an embodiment herein;

FIG. 14 illustrates COFIP patterns with 8 pilots, according to anembodiment herein;

FIG. 15 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 0 for AAS subframe with 6 OFDM symbols, accordingto an embodiment herein;

FIG. 16 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 1 for AAS subframe with 6 OFDM symbols, accordingto an embodiment herein;

FIG. 17 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 2 for AAS subframe with 6 OFDM symbols, accordingto an embodiment herein;

FIG. 18 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 0 for AAS subframe with 5 OFDM symbols, accordingto an embodiment herein;

FIG. 19 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 1 for AAS subframe with 5 OFDM symbols, accordingto an embodiment herein;

FIG. 20 illustrates COFIP pilot locations and pilot pattern assignmentsfor pilot pattern set 2 for AAS subframe with 5 OFDM symbols, accordingto an embodiment herein;

FIG. 21 illustrates a PRBS Generator with polynomial X³+X+1, accordingto an embodiment herein;

FIG. 22 illustrates Cellular Layout with reuse 7 pilot planning,according to an embodiment herein;

FIG. 23 illustrates CDR encoding with two transmitters, according to anembodiment herein;

FIG. 24 illustrates CDR region, according to an embodiment herein;

FIG. 25 illustrates CDR encoding within a PRU, according to anembodiment herein;

FIG. 26 illustrates CDR encoding using a pair of PRUs, according to anembodiment herein;

FIG. 27 illustrates multi-antenna precoding operation, according to anembodiment herein;

FIG. 28 illustrates baseband operations, according to an embodimentherein;

FIG. 29 illustrates a multi-antenna receiver, according to an embodimentherein;

FIG. 30 illustrates a CDR multi-antenna receiver, according to anembodiment herein;

FIG. 31 is a flow chart depicting a method showing the steps involved ina multi-antenna receiver utilizing COFIP, according to an embodimentherein;

FIG. 32 is a flow chart depicting a method showing the steps in a CDRmulti-antenna receiver utilizing COFIP, according to an embodimentherein; and

FIG. 33 illustrates CQI computation for subbands and minibands,according to an embodiment herein.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

The embodiments herein achieve a method for reducing interference atpilot symbols and also enable good interference measurements, enableefficient interference suppression receivers, accurate channel qualityinformation (CQI), estimation based on post-processed SINR, and as aresult enable accurate and efficient multi-user scheduling for CDR andnon-CDR modes operating in rank-1 OL region. However, this invention isnot limited to the rank-1 OL region. Referring now to the drawings, andmore particularly to FIGS. 1 through 33, where similar referencecharacters denote corresponding features consistently throughout thefigures, there are shown preferred embodiments.

Embodiments herein propose a way of reducing interference at pilotsymbols and also enable good interference measurements. The pilot designis based on the following design criteria:

1) Clusters of N sectors are numbered from 0 to N−1 called as sectornumbers. The N sectors can be derived from the cell/sector ID or BS IDusing modulo N operations, or by some other means. Where N can be anyinteger.

2) Each sector with a given sector number is assigned a pilot pattern.The pilot pattern assigned to each sector avoids pilot on pilotcollisions during pilot tone transmissions with any other sector havinga different sector number.

3) A Sector with a given sector number avoids interference, to thepilots of other sectors with a different sector number, by nottransmitting data or pilots at those locations corresponding to theirpilot pattern.

Essentially, a system with “N” transmitters is considered. When a giventransmitter transmits a pilot signal over a predefined time-frequencyresource, all other transmitters remains silent. The receivers canestimate the channel state information without any interference from theremaining N−1 transmitters and at the same time the receiver can measureeither the individual interference channel states or the interferencecovariances from the N−1 silent periods. The groups of “N” transmittersare reused in geographically separated region using a frequency reusestructure. In another embodiment, the pilot signal is precoded using amulti-antenna precoder. The precoder is preferably the same for pilotand data.

In an embodiment if N=3, a predetermined set of PRUs may transmit nulltones in the pilot locations of BSs having a Cell_ID different from theBS of the PRU. Null tones are introduced in the 1-stream interlacedpilot pattern as shown in FIGS. 8, 9 and 10. The index of the COFIP typeused by a particular BS with Cell_ID=k is denoted by p_(k). The index ofthe COFIP type is determined by the Cell_ID according to the followingequation: p_(k)=mod (k, N). The cell ID of the sectors in the same cellare contiguous numbers and there are three sectors per cell, andstandard reuse ⅓ sector planning is assumed. In another embodiment, theindex of the COFIP type can be determined by the Cell_ID according tothe following equation: p_(k)=floor (k/256). In this embodiment the cellIDs of the sectors in the same cell have a separation of 256, for e.g.,0, 256 and 512 are the cell IDs of the sectors in the same cell, andstandard reuse ⅓ planning is assumed.

In FIGS. 8, 9 and 10, ‘P’ denotes a pilot tone and ‘X’ denotes a nulltone i.e., no data or pilot tone is transmitted in that location. Nulltones reduce the interference level on the pilot locations. Null tonesalso facilitate measurements related to interference channels.

There is an even number of data tones in an OFDM symbol per Resourceblock (RB) (for example, 14 or 16). Sub-carrier pairs can be allocatedin the ‘frequency first’ manner, complying with the 802.16m sub-carrierpermutation. Each sub-carrier pair can contain SFBC ([s₁(−s₂*)s₂(s₁*)],CDR ([s₁s₂*]), or non-CDR etc.

The 6 ‘pilots+null tones’ in the 8^(th) and 9^(th) sub-carriers can bemoved up, down or to the right, with a constraint of even number ofsub-carriers in each symbol per RB. Let (x, y) be the location of apilot/null tone, where x is the symbol and y is the sub-carrier indices.The locations of 6 pilots/null tones in the 8^(th) and 9^(th)sub-carriers are (1,8),(1,9),(3,8),(3,9),(5,8) and (5,9).

Many variations in these pilot locations can be suggested in order tooptimize the channel estimation at different time and frequencyselectivity factors. The possible variations in the locations ofpilot/null tones can be represented as: (1+δ_(t),8+δ_(f1)),(1+δ_(t),9+δ_(f2)),(3+δ_(t),8+δ_(f3)),(3+δ_(t),9+δ_(f4)),(5+δ_(t),8+δ_(f5)), (5+δ_(t),9+δ_(f6)), where,δ_(t)ε{0, 1} and δ_(f)ε{−3,−2,−1,0,1,2,3}.

For the sub-frame consisting of 5 symbols, the last OFDM symbol in eachpilot pattern set shown in FIG. 8,9,10 can be deleted to form the newpattern. In another embodiment, the last OFDM symbol in each pilotpattern set shown in FIGS. 8, 9 and 10 are deleted and the pilot/nulltones are moved inside as shown in FIGS. 11, 12 and 13.

For the sub-frame consisting of 7 symbols, the first OFDM symbol in eachpilot pattern set shown in FIGS. 8, 9 and 10 is added as 7th symbol. Inanother embodiment, a pilotless OFDM symbol are added to the pattern setshown in FIGS. 8, 9 and 10, as 7 th symbol.

Other variation of COFIP is obtained by keeping the number of data tonesin an OFDM symbol per Resource block (RB) of size 18×6 an even number(e.g. could be 14 or 16 or 18), and the number of pilot tones could befour or six or eight. The COFIP pattern for 18×5 and 18×7 is obtainedfrom the 18×6 COFIP pattern by deleting any one column and adding anyone column, respectively. In FIG. 14, an alternative COFIP structurewhich contains 8 pilot tones in each PRU is shown. In FIG. 14, thepilots and null tones in a given row can be shifted up or down togenerate other variations.

Embodiments herein facilitate different reuse pattern for pilots anddata. In OFDMA systems, although pilots and data tones are transmittedin the same PRU, pilot tones can use reuse 1/M1 and data can use reuse1/M2. In another embodiment, pilots uses reuse ⅓ and data uses reuse 1.In yet another embodiment, pilots can use reuse factors ¼ or ⅕ or ⅙ or1/7 or 1/12. With lower reuse, quality of channel and covarianceestimates approach near ideal values. For example, quality of channeland covariance estimates approach “n”. The interference to the pilottones from the data tones of the other sectors is completely avoided. Asector transmits null tone at the tone locations corresponding to thepilot pattern assigned to other sectors having different sector number.The method has two key advantages.

1) The pilot tones are almost interference free except weak interferencefrom the pilot tones transmitted by those sectors with same sectornumber. The improved SINR at the pilot tones improve the accuracy ofchannel estimates

2) The tone locations corresponding to the pilot pattern assigned toother sector numbers may be used to get accurate interference covarianceestimates or channel estimates of dominant interferers as well asresidual interference covariance at those frequency locations. Thisinformation can be used either to construct the interference covarianceexplicitly, or use a demodulator that jointly detects the signal anddominant interferers while pre-whitening the residual interference.

The structure can be used in both UL and DL. The structure isparticularly useful in OFDMA based standards for improving channelestimation and interference suppression.

CDR feature can be implemented in OFDMA networks in a rank-1 OL CDRregion allocated to serve cell edge users and/or control channeltransmission. The network assigns a pre-defined rank-1 OL region usedfor CDR encoding either in DL or UL. CDR region may be composed of apredefined set of resource units (e.g., a predefined set of either PRUs,or slots, or tiles be reserved for CDR) in each BS in the network. FIG.24 illustrates the CDR region. Information about CDR region may becommunicated to each MS in a broadcast control channel.

In rank-1 OL CDR region, the data and its complex conjugate are mappedto a pair of subcarriers within a basic CDR resource unit. The basic CDRresource unit may be composed of one or several PRUs 2401/RBs/tiles andthe PRUs 2401/RBs/tiles may be contiguous or distributed intime-frequency plane. Mapping of complex and complex conjugate copies ofdata on to any two subcarriers is denoted as CDR encoding operation. Thesame type of CDR encoding is applied synchronously in all BSs in the CDRregion. When the desired signal is transmitted in symbol pairs as [D,D*] on any two subcarriers, the same CDR encoding operation is performedon the same pair of subcarriers in all BSs (or sectors) whiletransmitting the data. CDR feature can be implemented either in DL or ULor both in DL and UL independently. When CDR is implemented in UL, allusers in the network allocated in the CDR region use the same CDRencoding operation.

In FIG. 25 the basic CDR resource unit is one PRU and the complex andcomplex conjugate data pair denoted as [D, D*] is mapped to any twosubcarriers within that PRU. Certain subcarriers are reserved for pilottones. The pilot tones preferably use real-valued modulation such asbinary phase shift keying (BPSK), BPSK pilots aid in interferencecovariance estimation. If pilots use complex modulation, the pilots arealso transmitted in conjugate pairs to facilitate interferencecovariance estimation at the receiver.

In FIG. 26 the basic CDR resource unit is a PRU pair and a set of datasubcarriers are transmitted in the first PRU and the complex-conjugatecopies of the data contained the first PRU1 2601 are transmitted in thesecond PRU2 2602. The first and second PRUs may be contiguous PRUs intime, or frequency. The first and second PRUs may also be distributedanywhere in the time-frequency grid. Pilot tones may also be transmittedin conjugate pairs. A first set of pilot tones are transmitted in thefirst PRU, and its complex-conjugated copy is transmitted in the secondPRU.

In TREE 802.16m where the DL uses OFDMA, the basic CDR resource unit maybe chosen to be a single PRU composed of 18 subcarrier and 6 OFDMsymbols, or the PRU may be composed of 18 subcarrier and 5 OFDM symbols,or the PRU may also be composed of 18 subcarrier and 7 OFDM symbols. Ineach PRU of the 16m CDR region, the complex modulation symbol and itscomplex-conjugated copy are transmitted on a pair of subcarriers. Thepair of subcarriers may be adjacent in time or frequency. Certainsubcarriers are reserved for pilot tones. The pilot tones preferably usereal-valued modulation such as binary phase shift keying (BPSK). BPSKpilots aid interference covariance estimation. If pilots use complexmodulation, then the pilots are also transmitted in conjugate pairs tofacilitate interference covariance estimation at the receiver. In anembodiment, CDR region uses Collision Free Interlaced Pilot (COFIP)pilot structure. In each PRU employing COFIP pilots, the data and itscomplex conjugate are mapped together in adjacent OFDM subcarriers. Datamapping avoids pilot and null tones.

In rank-1 OL CDR region, the receiver receives a CDR encoded desiredsignal and several CDR encoded interferers. After collecting thereceived signal from multiple subcarriers and performing the conjugationoperation in those subcarriers used to send conjugated data, the signalreceived on each receiver antenna contains two copies of signal andinterference data undergoing distinct channels. With Nr receiverantennas, the CDR encoded signal gives 2*Nr copies of the signal. Areceiver processes the 2*Nr signal samples to reduce interference. In anembodiment, each of the 2*Nr received signal is filtered and combined toobtain a decision metric for demodulation. Filtering includes weighingof the received signal with a real/complex weight and summing up theweighted signals to obtain a decision metric for demodulation. Theweights are obtained by minimizing the mean-square-error or bymaximizing the post-processing SINR of the receiver. Computation ofweights takes into account an estimate of the channel state informationof the desired signal and covariance of the CDR encoded interferenceplus background noise. The filtered signal is used for demodulation oftransmitted modulation data.

FIG. 30 illustrates the receiver structure for 2-receiver antenna case.In the figure the symbol ( ) 3001 denotes complex conjugation operation.FIG. 30 shows a CDR receiver structure when pilot tones are modulated byreal-valued modulation such as BPSK. Since pilot tones use real-valuedmodulation, at each receiver antenna, collecting the complex valuedreceived pilots, and the complex conjugate of the received pilot signalgenerates two distinct copies of signal and interference. Collecting thepilot samples from all receiver antennas provides 4 copies altogether.The pilot samples are used to estimate the channel state information andthe covariance of the thermal noise plus total interference and theinformation is used to obtain the filter weights as well as CQI.

FIG. 31 is a flow chart depicting a method showing the steps involved ina multi-antenna receiver utilizing COFIP. If pilots use real-valuedmodulation such as BPSK, the receiver first performs 2D-MMSE channelestimation in conventional manner. The receiver uses the estimatedchannel states (3101) and the knowledge of known pilots to construct thedesired pilot signal. The reconstructed pilot (3102) signal issubtracted (3103) from the received pilot signal to obtain theinterference samples. Since interference also uses real-valued pilots,the receiver collects the complex and complex conjugate copies of theinterference samples and uses them for covariance estimation of the CDRencoded interferers contained in the pilot samples. This covarianceestimate is designated as first covariance estimate. In the second step,the interference samples are collected from the first set of null tonescontaining interference from sectors with same cell ID. Thecomplex-conjugated copy of the interference samples is collected. Boththe observations are used to construct a second interference covarianceestimate.

In the third step, the interference samples are collected from thesecond set of null tones containing interference from sectors with samecell ID. The complex-conjugated copy of these interference samples arethen collected and both the observations are used to construct a thirdinterference covariance estimate (3104). In another embodiment, all thethree covariance estimates are combined (3105) to estimate the totalcovariance. The receiver uses the estimated channel and the totalcovariance to obtain a set of weights for filtering. In otherembodiments, covariance estimate from pilot signal may not be used toobtain the total covariance. In COFIP mode, if pilots are transmitted inconjugate pairs, covariance estimation step uses the complex and complexconjugate copies of the interference samples for estimation. CDRreceiver generally suppresses 2Nr−1 interferers in a distributed mode.However with localized post-processing SINR based multi-user scheduling(such as proportional fair scheduling), the scheduler quite oftenselects a user in a certain sub-band where CDR encoded signal andinterference channels combines (or aligns) in such a manner that leadsto suppression of more than 2Nr−1 interferers. OL CDR region with fixedset of rank-1 precoders along with post-processed SINR scheduling canhandle more than 5-6-dominant interferers. Since, COFIP pilot structureensures accurate estimates of CQI through accurate channel andinterference covariance measurement, the base station will be able toperform scheduling and MCS allocation accurately.

In another embodiment COFIP is used in rank-1 OL region without CDRencoding. While OL region provides a stable interference environmentwith fixed multi-antenna precoders, the multi-antenna MMSE-type receiverprovides high interference suppression gain in both sub-band localizedand mini-band distributed modes. Especially in localized mode wherescheduling is based on the post-processed SINR of the MMSE receiver, thescheduler tends to allocate users with high SINR (or CQI) highinterference suppression gain. Although conventional MMSE receiver canonly suppress Nr−1 interferers in a conventional system, localizedpost-processing SINR based scheduling quite often selects a user in acertain sub-band in which signal and interference channels combines (oraligns) in such a manner that leads to suppression of several dominantinterferers. OL region with fixed set of rank-1 precoders along withpost-processed SINR schedules can handle more than 2-dominantinterferers. COFIP pilot structure is an important element in realizingthe full benefit of rank-1 OL region with post-processing SINR basedmulti-user scheduling.

FIG. 29 illustrates conventional multi-antenna MMSE type receiver. Inthe figure the symbol ( )* 3001 denotes complex conjugation operation.In rank-1 OL region, the receiver receives a rank-1 precoded desiredsignal and several rank-1 precoded interferers. Each of the Nr receivedsignals are filtered and combined to obtain a decision metric fordemodulation. Filtering includes weighing of the received signal with areal/complex weight and summing up the weighted signals to obtain adecision metric for demodulation. The weights are obtained by minimizingthe mean-square-error or by maximizing the post-processing SINR of thereceiver. Computation of weights takes into account an estimate of thechannel state information of the desired signal and covariance of therank-1 precoded interferers plus background noise. The filtered signalis used for demodulation of transmitted modulation data. FIG. 29illustrates the receiver structure for 2-receiver antenna case.

The receiver first performs 2D-MMSE channel estimation in conventionalmanner. Referring to FIG. 31, in each sector, null tones are depictedwith grey background denote first set of null tones and null tones aredepicted without grey background denote second set of null tones. InCOFIP mode, interference covariance is estimated in several steps. Thereceiver uses the estimated channel states (3201) and knowledge of knownpilots to construct the desired pilot signal. The reconstructed pilotsignal (3202) is subtracted (3203) from the received pilot signal toobtain the interference samples. This covariance estimate is designatedas first covariance estimate. The interference samples collected fromthe first set of null tones which contain interference from sectors withsame cell ID. Both observations are used to construct (3204) a secondinterference covariance estimate. The interference samples collectedfrom the second set of null tones contain interference from sectors withsame cell ID. Both observations are used to construct (3205) a thirdinterference covariance estimate. In an embodiment, all the threecovariance estimates are combined to estimate the total covariance(3206). Receiver uses the estimated channel and the total covariance toobtain a set of weights for filtering. In some embodiments, covarianceestimate from pilot signal may not be used to obtain the totalcovariance.

The interference cancellation gain of the MMSE receiver is highlydependent on the quality of the ‘interference plus noise’ covariancematrix estimate. A particular low-complexity method for estimating‘interference plus noise’ covariance matrix is described as follows:

y_(m,k,n) is the measured signal at n^(th) receiver antenna at thek^(th) pilot location corresponding to the sector number in.I_(m,k,n) is the interfering signal at n^(th) receiver antenna at thek^(th) pilot location corresponding to the sector number m.H_(k,n) is the fading channel coefficient at n^(th) receiver antenna atthe k^(th) pilot location of the desired sector.P_(k) is the pilot tone transmitted by the desired sector at the k^(th)pilot locationC is the Interference plus noise Covariance matrix.MaxSecNo is equal to N−1, where N is the number of sectors in a cellmySecNo is the desired Sector number of the subscriberNoPilots is equal to the number of pilots with in a PRUN_(r) is the number of Receiver antennae

The interference samples of the desired sector at each pilot locationare obtained by removing the signal component from the received signal.The interference samples of the desired sector at each pilot location isgiven by I_(m,k,n)=y_(m,k,n)−H_(k,n)*P_(k);

In CDR mode, the interference sample and its complex conjugate arecollected in a column vector format. The interference covariance matrixis estimated at all the pilot locations from the samples thus obtainedfor the desired sector. The interference covariance of the remainingsectors with different number is estimated from the received samples attheir pilot locations. The interference covariance obtained using theabove steps are added to get the overall interference covarianceestimate.

For m = 0 : MaxSecNo { if(m == mySecNo ) { For k = 0 : NOPilots { I_(m,k,n) = y _(m,k,n)− H _(k,n)*P _(k); I _(m,k) =[I _(m,k,0) I _(m,k,l)... I _(m,k,Nr−1)]^(T) if(CDRmode=on) I _(m,k) =[I _(m,k) conj( I_(m,k))]^(T) } C = C + I _(m,k) I _(m,k) ^(H) } } Else { I _(m,k,n) = Y_(m,k,n) I _(m,k) =[I _(m,k,0) I _(m,k,l) ... I _(m,k,nr−1)]^(T)if(CDRmode=on) I _(m,k) =[I _(m,k) conj( I _(m,k))]^(T) } C = C + I_(m,k) I _(m,k)H } }

The pilot structure in embodiments herein enables efficientimplementation of multi-user channel estimation and various advancedreceivers. For example, the channel state information of a set ofdominant interferers and residual noise-plus-interference covariance canbe estimated from the zero-tone locations. If the pilot sequences arepre-planned using a pilot planning method, then the pilots used by thedominant interferers is known a-priori to the receiver. The channelstates of various dominant interferers can be used in one of thefollowing implementations:

Construct the covariance of interference explicitly using the dominantinterfering channel state information and the residual covariances.

Use a multi-user joint demodulator preceded by a noise-whitening filterthat whitens the residual noise+interference.

The techniques are applicable to both CDR and non-CDR receivers

In an embodiment, OL rank-1 precoding and COFIP are employed togetherwith either CDR or non-CDR mode to obtain high interference suppressiongain. The output of the MIMO encoder is denoted as x which is a M_(t)×1vector. The output vector (N_(t)×1) of the precoder z=W,x. M_(t) is thenumber of MIMO streams, N_(t) is the number of transmit antennas, and Wis the N_(t)×M_(t) precoding matrix. In Rank-1 precoding and non-CDRtransmission, x is a scalar and W is the precoding vector. In the caseof CDR encoding, x=[s₁ s₁*] the modulation symbol s₁ is taken and sentalong with the complex conjugate of in s₁ consecutive subcarriers.

The MIMO schemes are suitable for cell-edge in reuse 1 cellular systemsbecause of their ability to suppress heavy interference with lowcomplexity. The COFIP pilot structure is very useful in both CDR as wellas non-CDR transmission because it enables the receiver to estimate thechannel, interference covariance, channel quality indicators (CQI) etc.accurately, even in the presence of heavy interference. This makes COFIPthe most suitable pilot structure for the cell-edge in reuse 1 cellularsystems.

In the downlink non-adaptive precoding, the W matrix for each Physicalresource unit (PRU) is selected in a fixed way by the Base station. In802.16m, the matrix W changes every N PRUs in frequency. Outside andinside the OL region N=N₁=4 and there is no change of precoders in time.This is called N₁ cycling. As the set of N₁ contiguous PRUs in frequencyis defined as a sub-band, the precoder is changed every sub-band. Theprecoding matrix W applied in physical subband ‘s’ is selected as thecodeword of index i in the codebook where i is given by: i=s mod N_(w),s=0, 1, . . . N_(sub)−1 where Nsub denotes the number of physicalsubbands across the entire system bandwidth. N_(w) is the number ofcodewords in the codebook.

In the OL region of type 1 with block distributed allocation, N=N2, andthe Nt×1 precoding matrix W applied in PRU ‘m’ in the subframe number‘t’ is selected as the codeword of index i in the codebook where i isgiven by

i=(m+(t mod 2))mod N _(w) m=0,1, . . . N _(PRU)−1.

In an embodiment, the index i is given by

i=(m)mod N _(w) , m=0,1, . . . N _(PRU)−1.

N_(PRU) is the number PRUs across the entire system bandwidth. As theset of N₂ contiguous PRUs in frequency is collectively defined as amini-band, the precoder is changed every mini-band.

The precoding matrix W is selected as the codeword of index i in thecodebook. For 2-Tx antennas, the elements of the code book may be chosenas:

${{C(1)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}}},{{C(2)} = {{\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}}.}}$

In an alternative embodiment, for 2-Tx antennas, the entries of the codebook C are given by:

${{C(1)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}}},{{C(2)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}}},{{C(3)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}}},{{C(4)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}}},{{C(5)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\\frac{1 + j}{\sqrt{2}}\end{bmatrix}}},{{C(6)} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\\frac{{- 1} - j}{\sqrt{2}}\end{bmatrix}}},{{C(7)}{\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\\frac{{- 1} + j}{\sqrt{2}}\end{bmatrix}}},{{C(8)}{{\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\\frac{{- 1} - j}{\sqrt{2}}\end{bmatrix}}.}}$

One may choose all the elements or certain sub set from the above codebook. In yet another embodiment, the following code book may be used:

${{C(1)} = \begin{bmatrix}1 \\0\end{bmatrix}},{{C(2)} = {\begin{bmatrix}0 \\1\end{bmatrix}.}}$

For 4-Tx antennas, single stream, transmission, the preferred entries ofthe code book are given by:

${{C(1)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}}},{{C(2)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\{- 1} \\1 \\1\end{bmatrix}}},{{C(3)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\j \\{- 1} \\j\end{bmatrix}}},{{C(4)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\{- j} \\{- 1} \\{- j}\end{bmatrix}}}$

In an alternative embodiment the following entries may be chosen forsingle stream 4-Tx case:

${{C(1)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\1 \\1 \\1\end{bmatrix}}},{{C(2)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\{- 1} \\1 \\{- 1}\end{bmatrix}}},{{C(3)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\1 \\{- 1} \\{- 1}\end{bmatrix}}},{{C(4)} = {\frac{1}{\sqrt{4}}\begin{bmatrix}1 \\{- 1} \\{- 1} \\1\end{bmatrix}}}$

For 4-Tx case one may use the code book with following elements:

${{C(1)} = \begin{bmatrix}1 \\0 \\0 \\0\end{bmatrix}},{{C(2)} = \begin{bmatrix}0 \\1 \\0 \\0\end{bmatrix}},{{C(3)} = \begin{bmatrix}0 \\0 \\1 \\0\end{bmatrix}},{{C(4)} = \begin{bmatrix}0 \\0 \\0 \\1\end{bmatrix}}$

The elements of code book for 8-Tx case may be chosen as:

${C(1)} = {\frac{1}{\sqrt{8}}\begin{bmatrix}1 \\^{{j\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j2\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j3\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j4\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j5\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j6\pi}\; {{Sin}{(\theta_{l})}}} \\^{{j7\pi}\; {{Sin}{(\theta_{l})}}}\end{bmatrix}}$${{{where}\mspace{14mu} \theta_{l}} = {{{\left( {\left( {l - 1} \right) + \frac{1}{2}} \right)\frac{\pi}{4}} - {\frac{\pi}{23}\mspace{14mu} {and}\mspace{14mu} l}} = 1}},2,\ldots \mspace{14mu},16$

More generally, one may use the following code book for Mt Tx antennas.The code book is a column vector of length Mt where the l'th element ofthe code book contains a 1 in the l'th row and all other elements arezeros.

Rank-1 OL-region uses one MIMO stream CDR encoding or non-CDR encoding.Localized and block distributed allocation of data is allowed in thisregion. Rank-1 OL MIMO region shall use Collision Free Interlaced Pilot(COFIP) pattern. FIGS. 8,9,10 shows the COFIP pattern for AAI subframesconsisting of 6 OFDM symbols. A predetermined set of PRUs may transmitnull tones in the pilot locations of BSS having a Cell ID which isdifferent from its own BS. Null tones are introduced in the 1-streaminterlaced pilot pattern as shown in FIGS. 8,9,10. The index of theCOFIP type used by a particular BS with Cell IDl=k is denoted by pk. Theindex of the COFIP type is determined by the Cell ID according to thefollowing equation:

$p_{k} = {{{floor}\left( \frac{k}{256} \right)}.}$

In another embodiment, the index of the COFIP type is determined by theCell ID according to the following equation:

p_(k)=mod(k,3). For AAI subframes consisting of 7 OFDM symbols, thefirst OFDM symbol which contains pilot tones and null tones in eachpilot pattern set shown in FIGS. 8,9, 10 is added as the 7th symbol.FIG. 11, 12, 13 shows the pilot pattern set for AAI subframes consistingof 5 OFDM symbols.

The pilot sequences assigned to different cells should have good crosscorrelation properties. For example, the PRBS generator shown in theFIG. 21 may be used to generate the pilot sequences for 802.16m singlestream pilot pattern. The characteristic polynomial for PRBS generatoris X³+X+1. The PRBS has a periodicity of 7 samples and only the first 6samples are used for deriving pilots since there are only 6 pilots within a PRU.

The pilot symbols P_(k) within a PRU are derived from W_(k) as followsP_(k)=(2*W_(k)−1)*sqrt(P_(s)) where P_(s) is the pilot tone power. Wherek=0 to 5. Different nonzero vectors [b₂ b₁ b₀] are used to initializethe PRBS generator in order to produce the code set C, which contains 7pilot sequences.

Pilot codebook P={P(0),P(1),P(2), P(3), P(4),P(5),) is defined in table1 where P(i), i=0,1 . . . , 5 denote the pilot values carried in a PRU.The location of the 6-pilot tones is shown in the COFIP pilot structurein FIGS. 15, 16 and 17 for AAI subframes with 6-OFDM symbols, and inFIGS. 18, 19 and 20 for AAI subframes with 5-OFDM symbols. For AAIsubframes consisting of 7 OFDM symbols, the first OFDM symbol whichcontains pilot tones and null tones in each pilot pattern set shown inFIGS. 15, 16 and 17 are added as the 7th OFDM symbol.

The PRBS generator can produce only 7 sequences with good crosscorrelation. Pilot planning is required to prevent two nearby basestations from using the same pilot sequence. For example a Reuse 1/7pilot planning as shown in FIG. 22 may be used. The cells marked by samenumber use the same pilot sequences. The seven cells are grouped into acluster and the cluster is repeated throughout the region.

TABLE 1 Pilot Modulation Sequences for COFIP Sequence Index PilotModulation sequence 0 [−1 −1 1 1 1 −1] 1 [−1 1 −1 −1 1 1] 2 [−1 1 1 1 −11] 3 [1 −1 −1 1 1 1] 4 [1 −1 1 −1 −1 1] 5 [1 1 −1 1 −1 −1] 6 [1 1 1 −1 1−1]

Pilot sequence cycling in time and/or frequency is implemented toexploit the advantage of interference averaging on the pilots The pilotsequences, generated in this way, which are used to modulate the COMPpilot subcarriers, shall be obtained from the set of pilot modulationsequences’ defined in Table 1. The sequence index used for modulation ofPRU pilot subcarriers is derived from i=mod(s+t+mod(mod(Cell ID 256),7),7), where ‘s’ is the physical PRU index, ‘t’ is the physical subframeindex. Alternatively, the base pilot code sequences to be used by an MScan be communicated in a control channel.

The CQI feedback together with the STC rate feedback (when applicable)composes the spectral efficiency value reported by the AMS. This valuecorresponds to the measured block error rate which is the closest, butnot exceeding, a specific target error rate. The Receiver computesChannel quality indicator (CQI) and feeds back to the BS. Usually, TheMS's preferred MCS level in a band is the CQI. In 802.16m. There are twomodes of CQI

1. Sub-band CQI, SB-CQI (for sub-bands)2. Wide Band CQI, WB-CQI (for mini-bands)The MS feeds back SB-CQI for all sub-bands and one WB-CQI in thefrequency partition where it is scheduled.

In the OL-region, as the precoders and the number of MIMO streams arefixed over time, the CQI computed using the output SINR's of thereceiver is very reliable. When a user is scheduled, the CQI availablefrom that user from its previous measurements is valid at the present.The only mismatch is from the channel/interference covariancemeasurement errors. The COFIP structure minimizes the errors. Thecombination of Open loop region and COFIP is very much suitable foraccurate CQI information at the Base station for efficient multi-userscheduling.

The CQI computation in the open-loop region involves the following steps

-   -   1. Compute post-receiver SINR at each tone (or tone pair, if        modulation symbols are spread over two subcarriers) for there        receiver under consideration i.e., CDR of non-CDR receiver.    -   2. Calculate an equivalent AWGN SINR from the set of SINRs        (which is computed in step 1) in the Resource Unit, using        methods like Avg SINR, RBIR or MMIB.    -   3. From the AWGN tables (SINR-BLER) of all the MCSs, find out        the best MCS which gives the maximum spectral efficiency and        satisfies BLER<BLER_(threshold)(BLER_(threshold)=0.1 or 0.01).

Spectral efficiency=log₂(Modulation size)*code rate*(1−BLER).

-   -   4. MS reports sub-band CQI for each sub-band in its frequency        partition and a single wide-band CQI for all the mini-bands.    -   5. In the case of N₁ cycling, where the precoder is fixed in        every subframe, CQI computation can be done using any one of the        subframes where precoded pilots are transmitted. In N₂ cycling,        the precoder is fixed in every 2 subframes, CQI computation can        be done using two consecutive subframes.

The DL OL region consists of a rank-1 OL MIMO region in which only asingle data stream is transmitted across multiple antennas and usessingle stream rank-1 OL precoding. The precoder is kept constant for theduration of the resource block (RB) and the precoder may change from oneresource block to another.

In the OL region, the precoder which is used in each RB is pre-defined.Data and pilots in each RB are precoded using the same precoder. In theOL MIMO region, in a predefined number of subframes, the dedicatedpilots shall be transmitted in each PRU even though data is notscheduled in that PRU. We refer to these pilots as “always ON” pilots.In the remaining sub frames, dedicated pilots shall be transmitted ineach PRU only if data is transmitted in that PRU.

The always ON pilot can be transmitted in the first or last “u”subframes of the allocated downlink frame. The value of “u” can be 0, 1,2 or 3. Or, the always ON pilots can be transmitted over any two “p”number of subframes in the allocated DL frame where p can take values 0,1, 2, or 3. Or, the pilots are ON in all the subframes allocated in theOL region, i.e., pilot tones are always transmitted even-though data isnot transmitted in those resources. The always ON pilot in selectsubframes concept can be used in CDR, OL multi-user (MU) MIMO. It canalso be used for SFBC/SM which is implemented in DRUs.

The receiver estimates channel quality information (CQI) using theprecoded pilots which are kept ON. The CQI is estimated as thepost-processing SINR of the receiver used by the MS. If the pilotstructure uses a combination of pilot tones and null tones, CQI can beestimated using the signal samples which received during the pilot tonesand null tones. The MS computes the best-band CQI for a set of sub-bands(best-M bands where the value of M is configured by the system) Candwideband CQI as well. This CQI information is feedback to the BS alongwith the indices of best sub bands. BS uses the CQI for multi-userscheduling and modulation and coding scheme (MCS) allocation. The regionin which the system uses dedicated pilots (pilots on only if data isON), the receiver preferably estimates the interference covarianceinformation from each RB independently. Since the number of interferersmay change from RB to RB it is preferable to confine interferencecovariance estimation to RB of interest. In other embodiments, therank-1 OL region may be divided into two regions: rank-1+COFIP+non-CDRregion and rank-1+CDR+COFIP regions. The system may employ both regionsat a time or one of the two regions at a time.

In rank-1 OL MIMO CDR region, the data its complex conjugate are mappedtogether in adjacent OFDM tones. The same encoding is applied in allbase stations synchronously across the network, OL rank-1 precoding isalso applied in all PRUs in the network. The precoder is pre-specifiedin this region. All PRUs transmitted in this region employs CDR encodingwith COFIP structure.

In rank-1 OL MIMO non-CDR region does use CDR encoding. In this region,OL rank-1 precoding is applied in all PRUs in the network. The precoderis pre-specified in this region. All PRUs transmitted in this regionemploys COFIP structure. In the subband mode, the MS reportspost-processing SINR (CQI) conventional MMSE receivers for best-M bandswhere M is an integer (set by the BS). Base station uses proportionalfair (PF) type scheduling to determine the user allocation in thesubbands. In the wideband mode, the MS reports post-processing SINR(CQI) of MMSE receiver for the allocated set of distributed min-bands.Base station uses proportional fair (PF) type scheduling to determinethe user allocation in the minibands based on wideband CQI.

In CDR region, in the subband mode, the MS reports post-processing SINR(CQI) of CDR MMSE receiver for best-M bands where M is an integer (setby the BS). Base station uses proportional fair (PF) type scheduling todetermine the user allocation in the subbands. In the wideband mode, theMS reports post-processing SINR (CQI) of CDR MMSE receivers for theallocated set of distributed min-bands. Base station uses proportionalfair (PF) type scheduling to determine the user allocation in theallocated min-band PRUs based on wide band CDR CQI.

Users with very low SINR and having interference from more than2-interferers can use CDR otherwise the user may be placed in non-CDRmode. The split between rank-1 and CDR region is done by BS in a semistatic manner. The resources which allocated for these regions aresignaled by the base station.

In some cases, the system may contain a mix of single and multi-antennatransmitters. In those cases, CDR and COFIP may be used in a rank-1region where MSs may use either OL or CL rank-1 precoders or a mix ofboth. This type of scenario typically happen in uplink. Similarly, onecan define a non-CDR COFIP region where either OL or CL or a mix of OLand CL transmissions are allowed.

The embodiments disclosed herein are not limited to cellular type systemwhere base stations communicate to mobile stations and vice versa. Theinventive concepts can be applied to communication between relays/Femtocells (or random networks) and mobile/nomadic receivers, or in systemswhere base stations, relays and Femtos co-exist in the same system. Insystems with large number of dominant interferers, reuse 6 or reuse 7COFIP is preferable for accurate CQI estimation. In random networks, thepilot interlace to be used in that base station/sector may be signaledto the MS explicitly in a control message.

In various embodiments, sector is not limited to a sector in cellularnetworks. A sector may be defined by any transmitter (including but notlimited to Femto cells and relays) covering an area around it. The areacovered may be partial (<360 degrees) or complete (360 degrees).

The embodiments disclosed herein can be implemented through at least onesoftware program running on at least one hardware device and performingnetwork management functions to control the network elements.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of theembodiments as described herein.

1. A method of enhancing interference mitigation in a wirelesscommunication network during transmission, said method comprising:assigning a unique pilot pattern corresponding to a sector identified bya sector number such that no two sectors with different sector numbershave pilots in same location in their respective pilot patterns, whereinsaid pilot pattern comprises of pilot tones and null tones.
 2. A methodas in claim 1, where in said network, a single data stream istransmitted across multiple antennas in each sector (or something likethat), where a pre-defined precoder is kept constant for the duration ofa Resource Block (RB) or groups of RBss, and where Data and pilots ineach RB are precoded using a same precoder.
 3. A method as in claim 2,wherein said communication network uses OL region.
 4. A method as inclaim 1, said method further comprising: repeating data symbols over oneor more subcarriers; encoding said repeated data symbols using any oneor both of complex conjugation and phase variation, wherein saidencoding of repeated data symbols is synchronized in multiple spatiallyseparated transmitters; and transmitting said repeated and encodedsymbols in each of said multiple transmitters in a synchronizedtransmission.
 5. A method as in claim 4, wherein said communicationnetwork uses OL region.
 6. A method as in claim 1, wherein OFDM symbol 7in a 7-symbol AAS (either call it AAS subframe of subframe consistently)subframe is same as first symbol in said 7-symbol subframe.
 7. A methodas in claim 1, wherein location of pilot tones and null tones in an RBmay be represented as (1,8),(1,9),(3,8),(3,9),(5,8) and (5,9).
 8. Amethod as in claim 1, wherein location of pilot tones and null tones inan RB may be represented as(1+δ_(t),8+δ_(f1)),(1+δ_(t),9+δ_(f2)),(3+δ_(t),8+δ_(f3)),(3+δ_(t),9+δ_(f4)),(5+δ_(t),8+δ_(f5)), (5+δ_(t),9+δ_(f6))), where,δ_(t)ε{0, 1} and δ_(f)ε{−3,−2,−1,0,1,2,3}.
 9. A method as in claim 1,wherein the last symbol in each pilot pattern is dropped, when subframeconsists of 5 symbols.
 10. A method as in claim 1, wherein number ofdata sub-carriers in each symbol in a resource block is even.
 11. Amethod as in claim 10, wherein when data appears in pairs, each pairappears in consecutive sub-carrers.
 12. A method as in claim 1, whereinnumber of data tones in a RB is even and number of pilot tones is one offour, six, and eight.
 13. A method as in claim 1, wherein in a subframewith 6 symbols, pilot tones and null tones may be used in a patternwhere, pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8),and (5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 14. Amethod as in claim 1, wherein in a subframe with 6 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 15. A method as in claim 1,wherein in a subframe with 6 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 16. A method as in claim 1, wherein in a subframe with 5symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 17. Amethod as in claim 1, wherein in a subframe with 5 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 18. A method as in claim 1,wherein in a subframe with 5 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 19. A method as in claim 3, wherein in a subframe with 6symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 20. Amethod as in claim 3, wherein in a subframe with 6 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 21. A method as in claim 3,wherein in a subframe with 6 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1.1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 22. A method as in claim 3, wherein in a subframe with 5symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 23. Amethod as in claim 3, wherein in a subframe with 5 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 24. A method as in claim 3,wherein in a subframe with 5 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 25. A method as in claim 4, wherein in a subframe with 6symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 26. Amethod as in claim 4, wherein in a subframe with 6 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 27. A method as in claim 4,wherein in a subframe with 6 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 28. A method as in claim 4, wherein in a subframe with 5symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 29. Amethod as in claim 4, wherein in a subframe with 5 symbols, pilot tonesand null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 30. A method as in claim 4,wherein in a subframe with 5 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 31. A method as in claim 5, wherein in a Advanced Air Interfacesubframe with 6 symbols, pilot tones and null tones may be used in apattern where, pilot tones occupy positions (1,1), (2,18), (3,9), (4,1),(5,8), and (5,18); and null tones occupy positions (1,8), (1,9), (1,18),(2,1), (3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).32. A method as in claim 5, wherein in a subframe with 6 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positrons (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 33. A method as in claim 5,wherein in a subframe with 6 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 34. A method as in claim 5, wherein in a subframe with 5symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18),(2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9). 35.A method as in claim 5, wherein in a subframe with 5 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 36. A method as in claim 5,wherein in a subframe with 5 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 37. A method as in claim 1, wherein pilots and data havedifferent reuse patterns.
 38. A method as in claim 1, wherein pilotsreuse is one among ⅓, ¼, ⅕, ⅙, 1/7, and 1/12, and data reuse is
 1. 39. Amethod as in claim 1, wherein for a predetermined number of subframes,dedicated pilots are transmitted in a PRU even though data is notscheduled, and in remaining subframes dedicated pilots are transmittedin a PRU only if data is scheduled.
 40. A method as in claim 39, whereinnumber of remaining subframes is zero.
 41. A method as in claim 3,wherein for a predetermined number of subframes, dedicated pilots aretransmitted in a PRU even though data is not scheduled, and in remainingsubframes dedicated pilots are transmitted in a PRU only if data isscheduled.
 42. A method as in claim 41, wherein number of remainingsubframes is zero.
 43. A method as in claim 4, wherein for apredetermined number of subframes, dedicated pilots are transmitted in aPRU even though data is not scheduled, and in remaining subframesdedicated pilots are transmitted in a PRU only if data is scheduled. 44.A method as in claim 43, wherein number of remaining subframes is zero.45. A method as in claim 5, wherein for a predetermined number ofsubframes, dedicated pilots are transmitted in a PRU even though data isnot scheduled, and in remaining subframes dedicated pilots aretransmitted in a PRU only if data is scheduled.
 46. A method as in claim45, wherein number of remaining subframes is zero.
 47. A method as inclaim 1, wherein pilot planning to prevent two adjacent base stationsfrom using same pilot modulation sequence comprises: assigning a pilotsequence of [−1 −1 1 1 1 −1] for a first sequence index; assigning apilot sequence of [−1 1 −1 −1 1 1] for a second sequence index;assigning a pilot sequence of [−1 1 1 1 −1 1] for a third sequenceindex; assigning a pilot sequence of [1 −1 −1 1 1 1] for a fourthsequence index; assigning a pilot sequence of [1 −1 1 4 −1 1] for afifth sequence index; assigning a pilot sequence of [1 1 −1 1 −1 −1] fora sixth sequence index; and assigning a pilot sequence of [1 1 1 −1 1−1] for a seventh sequence index.
 48. A method as in claim 1, wherein asequence index, which is to be assigned to a transmitter to find a pilotsequence to prevent two adjacent base stations from using same pilotmodulation sequence, is calculated using physical PRU index, physicalsubframe index, and cell ID of a particular base station.
 49. A methodas in claim 1, wherein a sequence index to be assigned to a transmitterto find a pilot sequence to prevent two adjacent base stations fromusing same pilot modulation sequence is given byi=mod(s+t+mod(mod(Cell ID,256),7),7), where ‘s’ is the physical PRUindex, ‘t’ is the physical subframe index, and Cell ID is a particularbase station.
 50. A method as in claim 1, wherein index of type of pilotpattern used by a transmitter is determined by floor(k/M), where k isthe cell ID corresponding to said transmitter, and M is the number ofcell sites.
 51. A method as in claim 1, wherein index of type of pilotpattern used by a transmitter is determined by mod(k,N), where k is thecell ID corresponding to said transmitter, and N is the number ofsectors per cell.
 52. A transmitter adapted for enhancing interferencemitigation in a wireless telecommunication network during transmission,said transmitter comprising at least one means for: assigning a uniquepilot pattern corresponding to a sector identified by a sector numbersuch that no two sectors with different sector numbers have pilots insame location in their respective pilot patterns, wherein said pilotpattern comprises of pilot tones and null tones.
 53. A transmitter as inclaim 52, where in said network, a single data stream is transmittedacross multiple antennas in each sector, where a pre-defined precoder iskept constant for the duration of a Resource Block (RB) or groups of RB,and where Data and pilots in each RB are precoded using a same precoder.54. A transmitter as in claim 53, wherein said communication networkuses OL region.
 55. A transmitter as in claim 52, said method furthercomprising: repeating data symbols over one or more subcarriers;encoding said repeated data symbols using any one or both of complexconjugation and phase variation, wherein said encoding of repeated datasymbols is synchronized in multiple spatially separated transmitters;and transmitting said repeated and encoded symbols in each of saidmultiple transmitters in a synchronized transmission.
 56. A transmitteras in claim 56, wherein said communication network uses OL region.
 57. Atransmitter as in claim 52, wherein symbol 7 in a 7-symbol subframe issame as first symbol in said 7-symbol subframe.
 58. A transmitter as inclaim 52, wherein location of pilot tones and null tones in an RB may berepresented as (1,8),(1,9),(3,8),(3,9),(5,8) and (5,9).
 59. Atransmitter as in claim 52, wherein location of pilot tones and nulltones in an RB may be represented as(1+δ_(t),8+δ_(f1)),(1+δ_(t),9+δ_(f2)),(3+δ_(t),8+δ_(f3)),(3+δ_(t),9+δ_(f4)),(5+δ_(t),8+δ_(f5)), (5+δ_(t),9+δ_(f6))), where,δ_(t)ε{0, 1} and δ_(f)ε{−3, −2,−1,0,1,2,3}.
 60. A transmitter as inclaim 52, wherein the last symbol in each pilot pattern is dropped, whensubframe consists of 5 symbols.
 61. A transmitter as in claim 52,wherein number of data sub-carriers in each symbol per resource block iseven.
 62. A transmitter as in claim 61, wherein when data appears inpairs, each pair appears in consecutive sub-carriers.
 63. A transmitteras in claim 52, wherein number of data tones in a RB is even and numberof pilot tones is one of four, six, and eight.
 64. A transmitter as inclaim 52, wherein in a subframe with 6 symbols, pilot tones and nulltones may be used in a pattern where, pilot tones occupy positions(1,1), (2,18), (3,9), (4,1), (5,8), and (5,18); and null tones occupypositions (1,8), (1,9), (1,18), (2,1), (3,1), (3,8), (3,18), (4,18),(5,1), (5,9), (6,1), and (6,18).
 65. A transmitter as in claim 52,wherein in a subframe with 6 symbols, pilot tones and null tones may beused in a pattern where, pilot tones occupy positions (1,9), (2,1),(3,8), (3,18), (5,1), and (6,18); and null tones occupy positions (1,1),(1,8), (1,18), (2,18), (3,1), (3,9), (4,1), (4,18), (5,8), (5,9),(5,18), and (6,1).
 66. A transmitter as in claim 52, wherein in asubframe with 6 symbols, pilot tones and null tones may be used in apattern where, pilot tones occupy positions (1,8), (1,18), (3,1),(4,18), (5,9), and (6,1); and null tones occupy positions (1,1), (1,9),(2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18), and(6,18).
 67. A transmitter as in claim 52, wherein in a subframe with 5symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 68. Atransmitter as in claim 52, wherein in a subframe with 5 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 69. A transmitter as in claim52, wherein in a subframe with 5 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 70. A transmitter as in claim 54, wherein in a subframe with 6symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 71. Atransmitter as in claim 54, wherein in a subframe with 6 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 72. A transmitter as in claim54, wherein in a subframe with 6 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 73. A transmitter as in claim 54, wherein in a subframe with5 symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 74. Atransmitter as in claim 54, wherein in a subframe with 5 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 75. A transmitter as in claim54, wherein in a subframe with 5 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 76. A transmitter as in claim 55, wherein in a subframe with 6symbols, pilot tones and null tones may be used in a pattern where,pilot tones, occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 77. Atransmitter as in claim 55, wherein in a subframe with 6 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 78. A transmitter as in claim55, wherein in a subframe with 6 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 79. A transmitter as in claim 55, wherein in a subframe with5 symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1); (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 80. Atransmitter as in claim 55, wherein in a subframe with 5 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 81. A transmitter as in claim55, wherein in a subframe with 5 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 82. A transmitter as in claim 56, wherein in a subframe with 6symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,18), (5,1), (5,9), (6,1), and (6,18).
 83. Atransmitter as in claim 56, wherein in a subframe with 6 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (5,1), and (6,18); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,18), (5,8), (5,9), (5,18), and (6,1).
 84. A transmitter as in claim56, wherein in a subframe with 6 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,18), (5,9), and (6,1); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), (5,18),and (6,18).
 85. A transmitter as in claim 56, wherein in a subframe with5 symbols, pilot tones and null tones may be used in a pattern where,pilot tones occupy positions (1,1), (2,18), (3,9), (4,1), (5,8), and(5,18); and null tones occupy positions (1,8), (1,9), (1,18), (2,1),(3,1), (3,8), (3,18), (4,8), (4,9), (4,18), (5,1), and (5,9).
 86. Atransmitter as in claim 56, wherein in a subframe with 5 symbols, pilottones and null tones may be used in a pattern where, pilot tones occupypositions (1,9), (2,1), (3,8), (3,18), (4,9), and (5,1); and null tonesoccupy positions (1,1), (1,8), (1,18), (2,18), (3,1), (3,9), (4,1),(4,8), (4,18), (5,8), (5,9), and (5,18).
 87. A transmitter as in claim56, wherein in a subframe with 5 symbols, pilot tones and null tones maybe used in a pattern where, pilot tones occupy positions (1,8), (1,18),(3,1), (4,8), (4,18), and (5,9); and null tones occupy positions (1,1),(1,9), (2,1), (2,18), (3,8), (3,9), (3,18), (4,1), (5,1), (5,8), and(5,18).
 88. A transmitter as in claim 52, wherein pilots and data havedifferent reuse patterns.
 89. A transmitter as in claim 52, whereinpilots reuse is one among ⅓, ¼, ⅕, ⅙, 1/7, and 1/12, and data reuseis
 1. 90. A transmitter as in claim 52, wherein for a predeterminednumber of subframes, dedicated pilots are transmitted a PRU even thoughdata is not scheduled, and in remaining subframes dedicated pilots aretransmitted in a PRU only if data is scheduled.
 91. A transmitter as inclaim 90, wherein number of remaining subframes is zero.
 92. Atransmitter as in claim 54, wherein for a predetermined number ofsubframes, dedicated pilots are transmitted a PRU even though data isnot scheduled, and in remaining subframes dedicated pilots aretransmitted in a PRU only if data is scheduled.
 93. A transmitter as inclaim 92, wherein number of remaining subframes is zero.
 94. Atransmitter as in claim 55, wherein for a predetermined number ofsubframes, dedicated pilots are transmitted a PRU even though data isnot scheduled, and in remaining subframes dedicated pilots aretransmitted in a PRU only if data is scheduled.
 95. A transmitter as inclaim 94, wherein number of remaining subframes is zero.
 96. Atransmitter as in claim 56, wherein for a predetermined number ofsubframes, dedicated pilots are transmitted a PRU even though data isnot scheduled, and in remaining subframes dedicated pilots aretransmitted in a PRU only if data is scheduled.
 97. A transmitter as inclaim 96, wherein number of remaining subframes is zero.
 98. Atransmitter as in claim 52, wherein pilot planning to prevent twoadjacent base stations from using same pilot modulation sequencecomprises: assigning a pilot sequence of [−1 −1 1 1 1 −1] for a firstsequence index; assigning a pilot sequence of [−1 1 −1 −1 1 1] for asecond sequence index; assigning a pilot sequence of [−1 1 1 1 −1 1] fora third sequence index; assigning a pilot sequence of [1 −1 −1 1 1 1]for a fourth sequence index; assigning a pilot sequence of [1 −1 1 −1 −11] for a fifth sequence index; assigning a pilot sequence of [1 1 −1 1−1 −1] for a sixth sequence index; and assigning a pilot sequence of [11 1 −1 1 −1] for a seventh sequence index.
 99. A transmitter as in claim52, wherein a sequence index, which is to be assigned to a transmitterto find a pilot sequence to prevent two adjacent base stations fromusing same pilot modulation sequence, is calculated using physical PRUindex, physical subframe index, and cell ID of a particular basestation.
 100. A transmitter as in claim 52, wherein a sequence index tobe assigned to a transmitter to find a pilot sequence to prevent twoadjacent base stations from using same pilot modulation sequence isgiven byi=mod(s+t+mod(mod(Cell ID,256),7),7), where ‘s’ is the physical PRUindex, ‘t’ is the physical subframe index, and Cell ID is a particularbase station.
 101. A transmitter as in claim 52, wherein index of typeof pilot pattern used by a transmitter is determined by floor(k/M),where k is the cell ID corresponding to said transmitter, and M is thenumber of cell sites.
 102. A transmitter as in claim 52, wherein indexof type of pilot pattern used by a transmitter is determined bymod(k,N), where k is the cell ID corresponding to said transmitter, andN is the number of sectors per cell.
 103. Method of implementing areceiver in a wireless communication network, said network using aunique pilot pattern corresponding to a sector number of a sector suchthat no two sectors with different sector numbers have pilots in samelocation in their respective pilot patterns, wherein said pilot patterncomprises of pilot tones and null tones, said method comprising:estimating channel; obtaining interference samples of desired sector ateach pilot location by removing signal component from received signal;estimating a first interference covariance at all pilot locations fromsaid samples for said desired sector; estimating a second interferencecovariance from null tones; adding said first and second interferencecovariances obtained to get overall interference covariance estimate;and determining weights for a filter at said receiver.
 104. A method asin claim 103, where in said network, a single data stream is transmittedacross multiple antennas in each sector, where a pre-defined precoder iskept constant for the duration of a Resource Block (RB) or groups ofRBs, and where Data and pilots in each RB are precoded using a sameprecoder.
 105. A method as in claim 104, wherein said communicationnetwork uses OL region.
 106. Method of implementing a receiver in awireless communication network, said network using a unique pilotpattern corresponding to a sector number of a sector such that no twosectors with different sector numbers have pilots in same location intheir respective pilot patterns, wherein said pilot pattern comprises ofpilot tones and null tones, said method comprising: estimating channel;obtaining interference samples of desired sector at each pilot locationby removing signal component from received signal; collectinginterference sample and its complex conjugate in a column vector format;estimating a first interference covariance at all pilot locations fromsaid samples for said desired sector; estimating a second interferencecovariance from null tones; adding said first and second interferencecovariances obtained to get overall interference covariance estimate;and determining weights for a filter at said receiver, where saidnetwork repeating data symbols over one or more subcarriers, andencoding said repeated data symbols using any one or both of complexconjugation and phase variation, where said encoding of repeated datasymbols is synchronized in multiple spatially separated transmitters.107. A method as in claim 106, where in said network a single datastream is transmitted across multiple antennas in each sector, where apre-defined precoder is kept constant for the duration of a ResourceBlock (RB) or groups of RBs, and where Data and pilots in each RB areprecoded using a same precoder.
 108. A method as in claim 107, whereinsaid communication network uses OL region.
 109. A receiver in a wirelesscommunication network, said receiver comprising at least one means forreceiving and demodulating signal transmitted in said network where aunique pilot pattern is assigned corresponding to a sector identified bya sector number such that no two sectors with different sector numbershave pilots in same location in their respective pilot patterns, whereinsaid pilot pattern comprises of pilot tones and null tones.
 110. Areceiver in a wireless communication network, said network using aunique pilot pattern corresponding to a sector number of a sector suchthat no two sectors with different sector numbers have pilots in samelocation in their respective pilot patterns, wherein said pilot patterncomprises of pilot tones and null tones, said receiver comprising atleast one means for: estimating channel; obtaining interference samplesof desired sector at each pilot location by removing signal componentfrom received signal; estimating a first interference covariance at allpilot locations from said samples for said desired sector; estimating asecond interference covariance from null tones; adding said first andsecond interference covariances obtained to get overall interferencecovariance estimate; and determining weights for a filter at saidreceiver.
 111. A receiver as in claim 110, where in said network, asingle data stream is transmitted across multiple antennas in eachsector, where a predefined precoder is kept constant for the duration ofa Resource Block (RB) or groups of RBs, and where Data and pilots ineach RB are precoded using a same precoder.
 112. A receiver as in claim111, wherein said communication network uses OL region.
 113. A receiverin a wireless communication network, said network using a unique pilotpattern col esponding to a sector number of a sector such that no twosectors with different sector numbers have pilots in same location intheir respective pilot patterns, wherein said pilot pattern comprises ofpilot tones and null tones, said receiver comprising at least one meansfor: estimating channel; obtaining interference samples of desiredsector at each pilot location by removing signal component from receivedsignal; collecting interference sample and its complex conjugate in acolumn vector format; estimating a first interference covariance at allpilot locations from said samples for said desired sector; estimating asecond interference covariance from null tones; adding said first andsecond interference covariances obtained to get overall interferencecovariance estimate; and determining weights for a filter at saidreceiver, where said network repeating data symbols over one or moresubcarriers, and encoding said repeated data symbols using any one orboth of complex conjugation and phase variation, where said encoding ofrepeated data symbols is synchronized in multiple spatially separatedtransmitters.
 114. A receiver as in claim 113, where in said network, asingle data stream is transmitted across multiple antennas in eachsector, where a predefined precoder is kept constant for the duration ofa Resource Block (RB) or groups of RBs, and where Data and pilots ineach RB are precoded using a same precoder.
 115. A receiver as in claim114, wherein said communication network uses OL region.
 116. Method ofcomputing Channel Quality Indicator at a receiver in a wirelesscommunication network, said network using a unique pilot patterncorresponding to a sector number of a sector such that no two sectorswith different sector numbers have pilots in same location in theirrespective pilot patterns, wherein said pilot pattern comprises of pilottones and null tones, said method comprising: computing post-receiverSINR for all tones.
 117. A method as in claim 116, said method furthercomprising: determining sub-band CQI for all sub-bands; and feeding backsaid sub-band CQI for all or best-M sub-bands along with the subbandindices of said best-M sub-bands.
 118. A method as in claim 116, saidmethod further comprising: determining wide band CQI; and feeding backsaid wide band CQI.
 119. A method as in claim 116, where in saidnetwork, a single data stream is transmitted across multiple antennas ineach sector, where a predefined precoder is kept constant for theduration of a Resource Block (RB) or groups of RBs, and where Data andpilots in each RB are precoded using a same precoder.
 120. A method asin claim 119, wherein said communication network uses OL region. 121.Method of computing Channel Quality Indicator at a receiver in awireless communication network, said network using a unique pilotpattern corresponding to a sector number of a sector such that no twosectors with different sector numbers have pilots in same location intheir respective pilot patterns, wherein said pilot pattern comprises ofpilot tones and null tones, said method comprising: computingpost-receiver SINR for all tone pairs spread over one or moresubcarriers, where said network repeating data symbols over one or moresubcarriers, and encoding said repeated data symbols using any one orboth of complex conjugation and phase variation, where said encoding ofrepeated data symbols is synchronized in multiple spatially separatedtransmitters.
 122. A method as in claim 121, said method furthercomprising: determining sub-band CQI for all sub-bands for distributedallocation; and feeding back said sub-band CQI for all or best-Msub-bands along with the subband with indices of said best-M sub-bands.123. A method as in claim 121, said method further comprising:determining wide band CQI for distributed allocation; and feeding backsaid wide band CQI.
 124. A method as in claim 121, where in saidnetwork, a single data stream is transmitted across multiple antennas ineach sector, where a pre-defined precoder is kept constant for theduration of a Resource Block (RB) or groups of RBs, and where Data andpilots in each RB are precoded using a same precoder.
 125. A method asin claim 124, wherein said communication network uses OL region.